Thermionic valve circuit



Jan. 30, 1934. A. WHITAKER THERMIONIC VALVE CIRCUIT Filed March 18, 1930m1 yE/v 70/? W m W, MW) A r rO/iNE'rS.

Patented Jan. 30, 1934 UNITED STATES PATENT OFFICE THERMIONIC VALVECIRCUIT Application March 18.

1930, Serial No. 436,874,

and in Great Britain April 8, 1929 4 Claims.

The present invention relates to thermionic valve circuits and moreparticularly to high frequency amplifier or detector circuits.

According to the present invention, in a thermionic valve circuit inwhich retroaction is provided between the anode and grid circuits of athermionic valve acting as a high frequency amplifier or detector, aresistance is connected in series between the anode of said valve andthe grid of a subsequent valve. The inclusion of this resistance permitsa substantially constant setting of reaction for all settings of thetuning condensers whilst the sensitivity of the circuit remainssubstantially constant.

The invention is illustrated by way of example in the accompanyingdrawing.

Referring to the drawing, an inductance l is connected between an aerialand an earth connection and is coupled to a second inductance 2 in thegrid circuit of a high frequency amplifier 3, this second inductance 2being tuned by means of a variable condenser 4 shunted across it. Theanode of the valve 3 is connected through a resistance 5, a reactioncoil 6 coupled to the coil 2 and a condenser 7, all arranged in series,to the grid of a second valve 8 which may be a second high frequenyamplifier or a detector valve. If desired, the valve 3 may be soconnected that it acts as a detector valve in which case the valve 8 maybe a low frequency amplifier. The side of the condenser '7 remote fromthe grid of the second valve 8 is connected through a tuned circuit 9comprising an inductance shunted by a variable condenser to the positiveterminal of a suitable high tension source 10, the negative terminal ofwhich is connected to one limb of the valve filaments. The couplingbetween the reaction coil 6 and the grid circuit of the first valve maybe made variable in known manner. It will be found that with the circuitabove described, if the value of the series resistance 5 is suitablychosen, the sensitivity of the circuit may be maintained substantiallyconstant throughout the range of the tuning condensers without alteringthe coupling between the reaction coil 6 and the tuned grid circuit 2,4.

It will be understood that the invention is not limited to circuitsembodying inductive reaction but is also applicable where capacityreaction is used. Furthermore, any desired form of coupling may be usedbetween one valve and the next in place of the tuned anode couplingabove described.

I claim:

1. In a thermionic amplifier, a pair of valves each having a tunableinput circuit, an output circuit for one of said valves connected to theinput circuit of the other valve, said connection including a radiofrequency current limiting resistor connected to the anode of the one orfirst valve, a stopping condenser connected to the rid of the other orsecond valve, and a feedback circuit connected in series between saidresistor and condenser.

2. In a thermionic amplifier, a first valve having a radio frequencyinput circuit, a second valve, a tunable circuit included in the outputcircuit for the first valve and serving as an input circuit for thesecond valve, and a series connection between said valves including aresistor connected to the anode of the first valve, a feed back inductorand a stopping condenser extending in series between said resistor andthe grid of the second valve, said resistor being located in said radiofrequency circuit whereby said resistor controls the flow of radiofrequency current therethrough.

3. In an electric amplifier, the combination of an electric valve, atuned grid circuit therefor, means providing a feed back coupling tosaid grid circuit connected with the anode of said valve, an outputcircuit coupling means for said valve connected in circuit and in serieswith said feed back coupling means to receive signal currentstherethrough from the anode, and a resistor interposed in circuitbetween the anode and said series connected coupling means to controlthe flow of current thereto from the anode.

4. In an electric amplifier, the combination of an electric valve, 21tuned grid circuit therefor, means providing a feed back coupling tosaid grid circuit connected with the anode of said valve, a tuned outputcircuit for said valve connected in circuit and in series with said feedback coupling means to receive signal currents therethrough from theanode, and a current limiting impedance means interposed in circuitbetween the anode and said feed back coupling means to control the flowof signal currents from the anode to said coupling means and throughsaid coupling means to the tuned output circuit.

ALFRED VII-IITAKER.

